How do I extract rows of a 2D NumPy array by condition?

Question

I have a 4*5 NumPy array and I want to retrieve rows in which all elements are less than 5.

arr = np.array([[0,2,3,4,5],[1,2,4,1,3], [2,2,5,4,6], [0,2,3,4,3]])
arr[np.where(arr[:,:] <= 4)]

expected output:

[[1,2,4,1,3],[0,2,3,4,3]]

actual output:

array([0, 2, 3, 4, 1, 2, 4, 1, 3, 2, 2, 4, 0, 2, 3, 4, 3])

Any help is appreciated!

user17242583 · Accepted Answer · 2022-02-07 02:31:41Z

1

This actually quite simple. Just convert the entire array to booleans (each value is True if it's less than 5, False otherwise), and use np.all with axis=1 to return True for each row where all items are True:

>>> arr[np.all(arr < 5, axis=1)]
array([[1, 2, 4, 1, 3],
       [0, 2, 3, 4, 3]])

answered Feb 7, 2022 at 2:31

user17242583

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